US 7503410 B2
A legged robot having a robot structure (20) in the form of a closed kinematic chain and an actuator (26) that contracts when activated. The contraction of the actuator extends a foot element (30) such that it can excerpt a pushing force against a ground surface. When the foot element excerpts sufficient force the legged robot can separate from the ground surface and achieve a dynamic hopping motion.
1. A robot comprising:
a. a robot structure comprising of links connected together with rotary pivots to form a closed kinematic chain;
b. an actuator that contracts when activated, the actuator comprising
a bladder, and
a sheath that constrains motion of the bladder;
c. a foot element connected to said robot structure; and
d. connections between said actuator and said robot structure such that when said foot element is placed in contact with a fixed object, and when said actuator is activated, then said foot element pushes against said fixed object.
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This application claims the benefit of and is a divisional application of U.S. patent application Ser. No. 11/068,243 filed on Feb. 26, 2005 now U.S. Pat. No. 7,168,513, which claims the benefit of and U.S. Provisional Patent Application No. 60/548,362 filed Feb. 27, 2004. The entire disclosure of the U.S. application Ser. No. 11/068,243 is incorporated by reference as part of the specification of this application.
This invention relates to mobile robots, specifically to legged robots.
The goal of developing a walking machine has been pursued since the late 1800s. One objective has been mobility, since the large majority of land is not reachable by wheeled and tracked vehicles. Other objectives include a greater understanding of biological systems and the design of human prostheses. And finally entertainment has always been a component of walking machine design.
Since the 1960s a number of successful walking machines have been built. A majority of these machines have four or more legs, and move in a quasi-static fashion meaning that at least three legs are kept on the ground at one time with the center of gravity of the robot kept within the region defined by the grounded feet. These robots move relatively slowly, and a large amount of computation is required to for leg placement over uneven terrain.
Marc Raibert, in Legged Robots That Balance, MIT Press (1986), describes dynamic legged robots that move in a fashion similar to fast moving biological animals where all legs can be in the air at the same time. Such dynamic robots have reached relatively high speeds of 21 km/h. However, one of the limiting factors of these robots, is that they must be plugged into the wall with a tether to a power source. These robots use electric motors, pneumatic actuators, and hydraulic actuators. The heavy weight of these actuators and power supply of such systems (e.g. batteries and hydraulic pumps) prevent dynamic hopping and running if they are carried on the robot. A robot that must be tethered to a power supply is significantly limited in its range of mobility.
Other legged robots have been developed that carry their own power supply and thus have increased mobility. The Honda Humanoid Robot (Kenji Kaneko et al. International Conference on Robotics & Automation, New Orleans, La., April 2004 pp. 1083-1090) carries its own batteries, but it does not exhibit highly dynamic motion, such as running or hopping where all legs are in the air simultaneously. The speed of the Honda Humanoid Robot is a relatively slow speed of approximately 2.5 km/h. Other robots, such as described by Paynter in U.S. Pat. No. 5,040,626 (1991), move in a quasi-static fashion and have gaits where multiple legs are in contact with the ground at all times; thereby limiting the speed of the robot.
Many legged robots have gaits where legs move back and forth during each stride. Therefore, these gaits require continual reversal of angular momentum of each leg, which reduces the top speed of the robot.
Accordingly, there is a need for a legged robot that can carry its own power supply and move at high speed with a dynamic gait. To achieve this objective there is a need for efficiency in the overall design of a robot. Specifically, there is a need that the robot actuators, power supply, structure, and control method all be designed for efficient high speed motion.
The present invention comprises a legged robot that can achieve high-speed dynamic motion, while carrying its own power supply, so that it can be un-tethered.
In addition to the object and advantages of the present invention described above, several objects and advantages of the present invention are:
a) Use of lightweight contractile actuators to reduce weight of a legged robot, and thereby reduce energy losses during impact with ground;
b) Use of compressed gas as a high power and light weight energy source, which enables dynamic motion;
c) A robot structure that has reduced structural loads, and thus can be light weight;
d) A robot structure with energy efficient joints;
e) A high speed legged gait;
f) Connections between actuator and robot structure that allow energy recovery during each gait cycle.
Further object and advantages will become apparent from a consideration of the ensuing description and drawings.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings, where:
120 robot structure 22 link 24 pivot 26 actuator 28 spring 30 foot element 32 ground 34 opposing spring 36 opposing foot element 38 platform link 40 gear teeth 42 connecting link 46 robot 100 contractile pneumatic 102 sheath actuator 104 bladder 106 end cap 108 hose connection 110 clamp 120 horizontal actuator 122 horizontal spring 124 vertical actuator 126 vertical spring 200 sensors 202 controller 204 actuators 206 stabilizing mass 208 stabilizing actuator 210 pressure vessel 212 valve 240 flexure pivot
A robot is a machine that includes the following components: structure, actuator, power source, sensor, and controller. A mobile robot is a robot that can travel from one location to another. The machines described herein are a class of mobile robots that use legs for locomotion. The following sections describe the various robot components that comprise the invention of a dynamic legged robot.
FIGS. 1 and 2A-2C—Embodiment of Robot Structure
A preferred embodiment of the robot structure 20 of the present invention is shown in
The steps in a dynamic hop of the robot is shown in
The foot element 30 is a part of the robot structure 20 that is designed to contact the ground and withstand impacts with the ground. The foot element 30 may be made of a material with a high coefficient of restitution to minimize energy loss during impact. Alternatively the foot element 30 may made of similar material and have a similar shape to other portions of the robot structure 20.
When the robot structure 20 is in a gravitational field and in contact with the ground 32, as shown in
A Closed Kinematic Chain is defined as a sequence of hinged bodies forming a loop. In the description herein, the hinges of a Closed Kinematic Chain refer to internal hinges of a structure. Thus, the statement that the robot structure is a Closed Kinematic Chain means that the internal components of the robot structure, including its links and pivots, form a Closed Kinematic Chain. Accordingly, the robot structure 20 shown in
An advantage of the robot structure shown in
An additional advantage of the robot described above is that the energy can be recovered during each hop; thereby increasing the energy efficiency of the robot. When the robot falls to the ground 32 the kinetic energy of the robot is transferred into potential energy of the springs 28 and the actuator 26. Thus the kinetic energy of the robot before it hits the floor, stretches the springs 28 and the actuator 26 during the impact with the ground 32. During the stage of bouncing upwards the energy stored in the springs 28 is transferred to the robot structure, thereby assisting the actuator 26 in propelling the robot upwards. The spring constants and inertia of the robot can be selected so that the natural frequency of the robot structure 20 is optimized for maximum energy recovery during each hop.
A preferred embodiment of the robot uses a contractile actuator to provide energy for locomotion and for hopping. An actuator transfers energy from an energy storage unit into the robot structure. A contractile actuator contracts in length when activated. A preferred type of contractile actuator for the robot is a Contractile Pneumatic Actuator as shown in
A Contractile Pneumatic Actuator is activated by flow of fluid into its bladder, where the fluid may be a gas or liquid. When fluid flows into the bladder, the internal volume of the bladder increases. The sheath of the Contractile Pneumatic Actuator constrains the motion of the bladder, causing the bladder to contract in length as its internal volume increases. In this fashion, the Contractile Pneumatic Actuator contracts in length when it is activated.
In embodiments where the Contractile Pneumatic Actuator has hose connectors 108 at both ends of the bladder 104, allow fluid to enter both ends of the actuator simultaneously. Alternatively, fluid may enter one end of the actuator and exit the other end.
Examples of Contractile Pneumatic Actuator include those described by: U.S. Pat. No. 6,349,746 to Bergemann et al. (2002); U.S. patent application Ser. No. 20,050,028,237 to Greenhill et al. (2005); U.S. Pat. No. 6,840,152 to Kriwet et al. (2005); U.S. Pat. No. 4,733,603 to Kukolj (1988); and U.S. Pat. No. 4,721,030 to Paynter (1988).
An advantage of Contractile Pneumatic Actuator is that as a contractile actuator, the components of the actuator are primarily in tension, and thus are not susceptible to bucking, which may occur if large compressive loads were present. Since buckling of the actuator is not likely, a contractile actuator can be made of components with relatively thin cross sections and thus be lightweight. An additional advantage of Contractile Pneumatic Actuator is that the use of pneumatic power allows for high power output with low weight energy storage.
FIG. 5—Alternative Spring Embodiment
An alternative embodiment shown in
The spring 28 connected in series with the actuator 26 can be comprised of a single spring element or multiple spring elements. The spring 28 can be a separate component or can be integrated into the actuator 26. Thus an actuator that extends when a tensile force is applied to it and stores energy in its internal structure due to work done by such a tensile force, functions as a spring as well as an actuator. Thus actuator 26 itself can serve as a spring, and be used to capture and release energy during each hopping step,
An alternative embodiment is to include torsion springs at all or some of the robot pivots 24. These torsion springs would increase the energy storage capability of the springs of the robot. In some embodiments, the torsion springs could replace all or some of the springs placed in series with the contractile actuator. The torsion springs could also replace all or some of the springs placed in opposition to the contractile actuator.
FIG. 6—Embodiment with Platform Link
The orientation of a robot or robot component can be defined relative to the locations of specified points on the robot or robot component. One method to specify the orientation of the robot structure 20 is relative to the location of the pivots 24 of the structure. When the location of pivots on a robot are symmetrical, then the orientation of the robot can be defined relative to an axis of symmetry of the pivots. In the embodiment shown in
An advantage of the embodiment shown in
In the embodiment shown in
Alternative embodiments include additional foot elements. Foot elements can be attached to any of the links of the robot structure. Foot elements can be attached to links whose orientation remains constant relative to the orientation of the robot structure, or foot elements can be attached to link whose orientation does not remains constant relative to the orientation of the robot structure
FIGS. 7 and 10—Robot Embodiment Including Stabilizing Mass, and a Control Block Diagram
An embodiment of a legged robot system is shown in
Stabilization and Orientation Control
For a single legged hopping robot, dynamic stabilization is required. One method for implementing such stabilization is to have a mass on the robot that is moved to provide reaction forces and torques on the robot and thereby generate the desired motion of the robot. In this fashion the robot can be stabilized to hop vertically or hop in a specific direction. The robot 46, can be controlled such that the point on the foot element which contacts the ground is substantially the same at different incidences of contact.
A block diagram of a control method is shown in
An embodiment that allows for control of the orientation of a legged robot 46 is shown in
When the stabilizing actuator 208 applies a torque and force between the stabilizing masses 206 and the robot structure 20, an equal an opposite torque and force is applied onto the robot structure 20. In this fashion the stabilizing masses can be used to control the orientation and motion of the robot. The stabilizing masses can be moved in the plane of the paper of the drawing of
Sensors 200 and a controller 202 can be attached to the robot structure 20 as shown in
The controller 202 can be a microprocessor, and an algorithm can be programmed into the microprocessor to define the necessary actuator commands necessary to provide a desired robot hoping performance and direction of travel.
For the purpose of control, it is desired to specify physical quantities such as angular velocity and angular momentum of a robot. The overall robot 46, has multiple components and indeed each link 22 may have a different angular momentum. However, the overall angular momentum of the robot is defined herein as the 3-dimensional vector sum of angular momentums of all the robot components. Furthermore, the angular velocity of the robot is defined herein as the overall angular momentum of the robot divided by the overall moment of inertia of the robot calculated about its instantaneous axis of rotation.
Source and Storage of Pressurized Gas
To activate a pneumatic actuator a source of pressurized gas or liquid is required. A method for providing pressurized gas for pneumatic robot actuators is to include a pressure vessel 210 on the robot such as shown in
In the embodiment shown in
To provide longer term operation of the actuator a chemical means of creating pressurized gas can be utilized. The chemical mean can include combustion as well as lower temperature reactions. Such chemical reactions can include the type described by Spletzer et al. in U.S. Pat. No. 6,247,546 (2001). The pressurized gas generated from these reaction can be stored in an intermediate pressure vessel, such as the pressure vessel 210 in
An alternative embodiment for attaching actuators to the robot structure for the purpose of changing the shape of the robot structure and moving the foot element is shown in
When the horizontal actuator 120 is actuated, the right and left side of the robot structure come together, resulting in a longer but thinner structure. When the vertical actuator 124 is actuated the top and bottom pivots are brought together, resulting in a shorter but wider structure.
Both vertical and horizontal actuators can be used to increase hopping height. The vertical and horizontal actuators can be activated according to the steps shown in the
The robot hop height depends in part upon how much energy can be transferred from the actuators, 120 and 124, and springs, 122 and 126, into the robot structure during the brief period during which the robot is in contact with the ground. By using both horizontal and vertical actuators, it becomes possible to apply power from the actuators during the downward motion of the robot as well as during the upward motion. Thus, it becomes possible to increase the energy transfer from the actuators into a hopping motion.
Two contractile actuators are defined herein to be configured in opposition when their configuration results in one actuator lengthening when the other actuator is contracted. In the embodiment shown in
A Contractile Pneumatic Actuator behaves partially as a spring in the sense that an external force that stretches a Contractile Pneumatic Actuator puts energy into the actuator. Accordingly, Contractile Pneumatic Actuators that are configured in opposition can transfer energy from one actuator to the other.
FIG. 11—Head-Over-Heals Gait
Traditional legged robots have a disadvantage relative to wheeled vehicles. In a wheeled vehicle, the wheels continually rotate in the direction of vehicle motion. Thus, the wheels can maintain a high angular momentum. And thereby allow for high-speed wheeled motion. However, with traditional legged robots each leg has a back and forth gait, which requires a reversal of the angular momentum of the legs and limits the total overall speed of the robot. The head-over-heels control approach shown in
The head-over-heels control approach is similar to a handspring of a gymnast. In the robot embodiment shown in
The head-over-heels gait can be applied to robot structures with just a single foot element or robot structures with more than two foot elements. For example, a foot element 30 could be located near each of the pivots 24 of the robot structure shown in
In a wheeled vehicles there is typically continual contact between the wheel surface and the ground. However, in the head-over-heals gait the contact between the robot and the ground or other surface occurs at discrete foot elements. In the head-over-heels gait the contact between one foot element and the ground can be followed by contact between a second foot element an ground, as shown in
In a traditional cart with wheels, the direction of rotation of the cart wheels can be defined such that is aligned with the direction of travel of the cart. The 3-dimensional angular velocity vector of a wheel on a traditional cart is perpendicular to the direction of travel of the wheel. In a similar fashion, the Direction of Rotation of a robot is defined herein to be perpendicular to the 3-dimensional angular velocity vector of the robot and parallel to the surface over which the robot is traveling. In the sequence shown in
FIG. 15—Embodiment of a Flexure Pivot
In the embodiments shown in
A flexure pivot, such as shown in
The use of flexure pivots in the robot embodiments described herein can decrease frictional losses, and thereby increase the efficiency of robot motion. Flexure pivots can be used in all or some of the pivots described herein.
Multi Legged Robots
The embodiments shown in Fig FIGS. 1,2,5-9,11 depict legged robots 46 that move as a single leg. Multi-legged robots can be built by combining the single leg embodiments described herein. For example there could be two legged, four legged, or six legged robots. An advantage of multiple legged robots is that they can stand in a stable configuration without motion thereby conserving energy. Thus a multi-legged robot can achieve higher energy efficiency, which would allow for longer range of motion of the robot. A multi-legged robot could be controlled in a dynamic fashion similar to running, trotting or galloping. Also a multi-legged robot could be controlled in less dynamic mode similar to walking.
Accordingly, the reader can see that the dynamic legged robot of this invention can be used to achieve high speed dynamic motion. These advantages include:
Use of contractile actuators in combination with a closed kinematic chain to reduce weight of the robot structure, and thereby reduce energy losses during impact with ground;
Use of lightweight pneumatic contractile actuators to reduce the weight of the robot and the energy source.
Use of opposing contractile actuators to increase power transfer between the robot and the ground during the time when the robot is in contact with the ground.
Use of flexure pivots to reduce energy loss and increase robot motion efficiency.
A high speed head-over-heels gait.